An analog-to-digital converter (Analog-to-Digital Converter, ADC) is a device converting an analog signal into a digital signal, and is widely applied to electronic products in fields such as meters, communication, signal detection, image processing, and multimedia. With the development of electronic products, requirements on precision, speed and power consumption of the ADC become higher and higher, and a comparator in the ADC has a crucial effect on the precision, speed and power consumption of the ADC. Therefore, how to reduce the power consumption of the comparator and improve the speed and precision of the comparator becomes the focus of research in recent years.
A circuit of a comparator in the prior art is shown in FIG. 1, where M5, M6, M7 and M8 are differential transistors, reference voltages are VREFP and VREFN, input voltages are VINP and VINN, and when VINP-VINN>VREFP-VREFN, current 113 flowing into M13 is greater than current 112 flowing through M12. Since M15 mirrors the current of M13, and M14 mirrors the current of M12, change of the input differential voltage signals VINP and VINN is converted into change of the currents of M12, M13, M14 and M15.
In a pre-amplifying circuit of the comparator in the prior art, the input voltage is converted into a current difference between M12 and M13. However, since M14 and M15 mirror the currents of M12 and M13, and meanwhile amplify the currents of M12 and M13, the currents of M14 and M15 are amplified and delivered to a next-level comparison circuit. The next-level comparison circuit obtains a comparison result of M14 and M15, and meanwhile, the power consumption of the comparator is increased by the amplified direct current bias current. In addition, M18 and M19 of the second level need to adopt higher specification to allow greater current to pass through due to the power consumption of the direct current, which causes the speed reduction of the comparator. Moreover, when a clock CLK is at a low level, it cannot be ensured that one of M18 and M19 is in a conduction state and the other is in a cutoff state, which further increases the power consumption of the comparator.